Journal of Geosciences, 65 (2020), 45–57

DOI: 10.3190/jgeosci.296

Original paper

New crystal-chemical data on zincoberaunite from Krásno near
Horní Slavkov (Czech Republic)
Jaromír TVRDÝ1*, Jakub PLÁŠIL2, Radek ŠKODA1
Department of Geological Sciences, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic;
jt.geologie@gmail.com
2
Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Na Slovance 2, 182 21 Prague 8, Czech Republic*
Corresponding author
1

A study of zincoberaunite from Krásno near Horní Slavkov (Czech Republic) provided new chemical and structural dataof this rare member of the beraunite group. The studied material is monoclinic, space group C2/c, with a = 20.3440(19) Å,
b = 5.1507(3) Å, c = 19.1361(15) Å, β = 93.568(8)°, V = 2001.3(3) Å3, Z = 4. Based on refined site occupancies and bond-valence considerations, the structural formula is (Zn0.81Al0.19)(OH)2(Fe0.61Al0.39)(OH)2(H2O)2(Fe1.52Al0.48)(H2O)2(Fe1.72Al0.28)(OH)(PO4)3.83(AsO4)0.17(H2O)2. Electron-microprobe analyses support the obtained results. However, keeping the samecation occupancy at the M2–M4 sites, the ratio of Al3+ to Me2+ at the M1 site requires the presence of divalent cations
as follows: (Zn0.57Fe0.24Al0.19)Σ1.00(Fe3.85Al1.15)Σ5.00[(PO4)3.89(AsO4)0.10(SiO4)0.01]Σ4.00[(OH)4.59F0.24 O0.17]Σ5.00(OH2)4.00·2H2O.
Individual prismatic zincoberaunite crystals exhibit a chemical zonation manifested by increasing Fe and decreasing
Zn and Al contents from cores to rims. The mineral composition is close to the Zn–Al-rich members of the beraunitegroup known from the same locality, but in this case, dominant occupancy of Zn at the M1 site was confirmed. With its
increased aluminium content, zincoberaunite from Krásno differs significantly from the holotype specimen described from
Hagendorf South pegmatite in Germany. The most prominent Raman bands are in good agreement with data publishedfor related members of the beraunite group. Structure refinement (R = 3.56 % for 1906 observed unique reflections)revealed three different types of OH or H2O, which play distinct role in structure bonding.
Keywords: zincoberaunite, phosphate, crystal structure, Raman spectra, Krásno near Horní Slavkov, Czech Republic
Received: 13 November 2019; accepted: 3 March 2020; handling editor: J. Cempírek
The online version of this article (doi: 10.3190/jgeosci.296) contains supplementary electronic material

1. Introduction

titioning behaviour in beraunite-type mineral structure;
crystal-structure refinement supplemented by quantitative electron-microprobe analyses (EPMA) and Raman
spectroscopy proved that while Zn2+ enters preferentially
the M1 site, Al3+ is not dominant at any specific position.
Therefore, the mineral can be classified as Al-rich zinco­
beraunite; results of our study are given in this paper.

Zincoberaunite is a member of the beraunitegroup of minerals with the general formula
M1M2M32M42(PO4)4(OH)5·6H2O. Currently, the beraunitegroup includes four members listed in Tab. 1. Zincoberaunite, ideally ZnFe3+5(PO4)4(OH)5·6H2O, was described
as a new mineral from the Hagendorf South granitic
pegmatite, Bavaria, Germany, few years ago (Chukanov
2. Occurrence
et al. 2016). A Zn- and Al-rich variety of beraunite wasobserved in Krásno near Horní Slavkov (Czech Republic)
The Sn–W ore district of Krásno–Horní Slavkov is ain 2006 already (Sejkora et al. 2006), but the contents offamous area of ancient mining in the Slavkovský lesboth elements were not high enough for definition of a
Mts., located in Western Bohemia, Czech Republic
new species. Average Zn contents in the holotype sample(Beran and Sejkora 2006). Mining activities since theof tvrdýite, ideally Fe2+Fe3+2Al3(PO4)4(OH2)4·2H2O, and12th century were documented there (Beran 1995). The
associated Al-rich beraunite from the same locality areore mineralisation is bound to greisenized cupolas of
0.52 and 0.64 apfu, respectively. However, there is no
Zn dominance at any specificsite and, moreover, Zn occu- Tab. 1 Members of the beraunite grouppies the M1, M3 and M4 sites Beraunite
Fe2+Fe3+5(PO4)4(OH)5·6H2O
Breithaupt (1840, 1841)
Fe3+6(PO4)4O(OH)4·6H2O
Chukanov et al. (2017)(Sejkora et al. 2016). In this Eleonorite
Fe2+Fe3+2Al3(PO4)4(OH)5(H2O)4·2H2O
Sejkora et al. (2016)
study of a sample from Krásno Tvrdýite
ZnFe3+5(PO4)4(OH)5·6H2O
Chukanov et al. (2016)
we present different cation par- Zincoberaunitewww.jgeosci.org

Jaromír Tvrdý, Jakub Plášil, Radek Škoda

Variscan granitic bodies emplaced into migmatised
Proterozoic paragneisses. These granitoids belong to thelarge composite batholith that underlies the entire Krušné
hory/Erzgebirge block in depth. The largest cupola is the
Huber Stock; its apical parts were completely metasomatised to a compact greisen with disseminated ore minerals(Jarchovský 2006). Greisens and surrounding gneisses
are penetrated by centimetre- to decimetre-thick quartz
veins often containing rich Sn–W mineralisation. Until
1991, the Stannum shaft and a small-open pit exploited
the Huber Stock.
Relatively common minor components of greisenbodies and associated quartz veins in the Krásno–Horní
Slavkov area are phosphate accumulations (Beran andSejkora 2006). Phosphate masses range from several
millimetres up to 1 m in size and consist of dominant
fluorapatite and triplite, occasionally also accompanied
by frondelite (Sejkora et al. 2006). Their late hydrothermal to probably supergene alterations led to the formationof a number of secondary mineral phases, including firstdescribed new phosphates iangreyite (Mills et al. 2011),
krásnoite (Mills et al. 2012), tvrdýite (Sejkora et al.
2016), and kenngottite (Sejkora et al. 2019b).
The studied specimen is 8 × 5 × 5 cm in size and wascollected in the Huber open pit during the last phase ofmining of Sn–W ores in the late 1980s. It is represented
by white, partly limonitised gangue quartz containing
fluorapatite of two different types, occurring as (i) several
fresh bottle-green isometric grains up to 7 mm and as(ii) an irregular fine-grained pinkish-beige aggregate ofc. 30 × 15 mm in size. Zincoberaunite occurs in a small
cavity (dimensions c. 15 × 10 mm) as thin acicular crystals grouped in radiating aggregates up to 2 mm in size.
The aggregates have a glassy lustre and are dark yellowish-grey in the centres, grading into yellowish-brownon the margins (Fig. 1). The specimen and the analysed
epoxy mount are stored in the research collection of thefirst author (JT) under the number T-121.

3. Chemical composition

Fig. 1 Zincoberaunite from Krásno, Czech Republic. Field of view is
4 mm wide.

Fig. 2 Electron-microprobe image (BSE mode) of zincoberaunite from
Krásno; individual analytical points are labelled with numbers.

46

The chemical composition of zincoberaunite was determined on polished and carbon-coated fragments mounted
in an epoxy cylinder using a Cameca SX 100 electron
microprobe (Joint laboratory of Masaryk University Brnoand of the Czech Geological Survey). The instrument was
operated in wavelength-dispersive mode at accelerating
voltage of 15 keV, beam current of 10 nA, and beam
diameter of 5 µm from 13 analytical points (Fig. 2). The
following X-ray lines and standards were selected; Kαlines: P (fluorapatite), Al (andalusite), K (orthoclase),
Zn (gahnite), Ni (syn. Ni2SiO4), Fe (ferrocolumbite), Mg(syn. Mg2SiO4), Na (albite), Si, Ca (wollastonite), Mn(spessartine), Ti (syn. TiO2), S (syn. SrSO4), Cl (vanadinite) and F (topaz), Lα lines: As, Cu (lammerite), Sr (syn.
SrSO4), Ba (baryte). Contents of Na, K, Ca, Mg, Ni, Cu,
Ba, Ti, S and Cl were below detection limits (~0.05–0.10
wt. %). Counting times were 10–20 s on peak and halfof this time for each background position. The measured
X-ray intensities were processed for matrix effects using
the X–φ correction routine (Merlet 1994). Water could
not be analysed directly because of the very small amountof material available; it was calculated on the basis of
17 H apfu from the crystal-structure analysis, corrected
for partial substitution of F and O for OH.
The chemical composition of zincoberaunite from
Krásno is given in Tab. 2, together with published datafor holotype samples of the same mineral (Chukanov
et al. 2016), tvrdýite and associated Al-rich beraunite(Sejkora et al. 2016). The analytical results show a slightchemical heterogeneity of the sample and are in a good
agreement with the crystal structure analysis (see below).
However, keeping the same cation occupancy in the

bdl.
bdl.
bdl.
5.45
1.92
35.82
8.04
bdl.
1.34
32.34
0.57
–0.24
17.42

bdl.
bdl.
bdl.
4.95
2.75
36.12
7.29
0.13
1.67
31.38
0.46
–0.19
17.05

5
bdl.
bdl.
bdl.
4.96
2.26
36.74
6.70
0.10
1.33
31.42
0.46
–0.19
17.04

6
bdl.
bdl.
bdl.
4.68
1.63
37.45
7.22
bdl.
1.40
32.54
0.72
–0.30
17.59

7
bdl.
bdl.
bdl.
6.31
2.35
33.35
8.81
0.11
1.03
31.53
0.43
–0.18
16.70

8

9

10

11

12

13

bdl.
bdl.
bdl.
5.24
1.60
34.49
8.62
bdl.
1.18
32.15
0.49
–0.21
17.42

bdl.
bdl.
bdl.
4.95
2.67
35.82
7.68
0.45
1.31
31.44
0.63
–0.27
17.16

bdl.
bdl.
bdl.
5.79
1.17
36.04
7.96
bdl.
1.43
32.35
0.48
–0.20
17.62

bdl.
bdl.
0.11
4.94
2.25
35.78
7.71
bdl.
1.29
31.99
0.26
–0.11
17.38

bdl.
bdl.
bdl.
5.80
2.04
34.41
8.39
0.12
1.33
31.61
0.54
–0.23
17.00
100.71
–
–
0.00
0.65
0.50
3.50
1.31
5.96
–
0.17
3.90
4.07
16.00
4.81
0.08
6.00

bdl.
bdl.
0.02
6.01
4.14
31.70
7.54
bdl.
2.19
31.39
0.17
–0.07
17.16

Sejkora et al.
(2016)

Al-rich beraunite**§Tvrdýite**

100.62
–
–
0.00
0.52
0.50
2.21
2.75
5.98
–
0.19
3.86
4.05
16.00
4.60
0.23
6.00

bdl.
bdl.
0.01
5.08
4.31
21.16
16.71
bdl.
2.56
32.64
0.53
–0.22
17.84

Sejkora et al.
(2016)

Fe2+/Fe3+ ratio on zincoberaunite from Krásno was estimated based on M1-site occupancy to keep the Al3+–R2+ proportions similar to the structural formula;
Fe2+/Fe3+ ratio of other phases was adopted from the references*
Calculation based on Si + As + P = 4 apfu, total H 2O content calculated on the basis of 6 H2O molecules and charge balance**
Calculation based on 27 anions per formula unit; H 2O on the basis of 17 H apfu, corrected for a partial substitution of F for OH
bdl. – below detection limit

bdl.
bdl.
bdl.
4.70
2.61
35.92
7.44
0.12
1.67
31.42
0.29
–0.12
17.23

4

101.73 102.62 102.64 101.38 102.91 101.77 100.98 103.38 100.6 101.18 102.08 102.83 101.67 101.22
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.013
–
0.568 0.682 0.555 0.503 0.573 0.530 0.535 0.489 0.681 0.556 0.527 0.608 0.526 0.621
0.235 0.119 0.156 0.316 0.229 0.333 0.276 0.193 0.288 0.192 0.322 0.139 0.272 0.247
3.846 3.774 3.710 3.919 3.840 3.943 4.037 3.986 3.671 3.730 3.885 3.856 3.881 3.756
1.344 1.416 1.480 1.271 1.350 1.247 1.153 1.204 1.519 1.460 1.305 1.334 1.309 1.434
5.993 5.991 5.901 6.009 5.992 6.053 6.000 5.872 6.159 5.938 6.039 5.936 6.000 6.058
0.012
–
–
0.017
–
0.019 0.015
–
0.016
–
0.065
–
–
0.017
0.102 0.081 0.122 0.127 0.100 0.127 0.102 0.104 0.079 0.089 0.099 0.106 0.097 0.101
3.886 3.919 3.878 3.856 3.900 3.854 3.884 3.896 3.905 3.911 3.836 3.894 3.903 3.882
4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000
16.165 16.171 16.000 16.190 16.174 16.278 16.176 16.000 16.493 16.066 16.202 16.063 16.165 16.289
4.594 4.377 4.728 4.677 4.569 4.511 4.612 4.612 4.308 4.711 4.511 4.722 4.717 4.464
0.241 0.452 0.264 0.133 0.257 0.211 0.212 0.322 0.199 0.223 0.287 0.216 0.118 0.248
6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000

bdl.
bdl.
bdl.
5.31
1.32
34.83
8.87
bdl.
1.65
32.36
0.59
–0.25
17.70

3

Total
Ca2+
Mg2+
Mn2+
Zn2+
Fe2+
Fe3+
Al3+
Σ
Si4+
As5+
P5+
Σ
O2–
OH–
F–
H 2O

bdl.
bdl.
bdl.
6.46
1.00
35.09
8.41
bdl.
1.09
32.39
1.00
–0.42
17.17

2

CaO
MgO
MnO
ZnO
FeO§
Fe2O3§
Al2O3
SiO2
As2O5
P 2O 5
F
F=O
H 2O

1

Mean
(n =
13)
bdl.
bdl.
bdl.
5.35
1.95
35.54
7.93
0.08
1.36
31.92
0.53
–0.22
17.29

Zincoberaunite, Krásno*

99.24
0.08
0.06
–
0.83
0.00
4.88
0.16
6.01
–
–
4.09
4.09
16.36
4.78
–
5.86

0.47
0.28
bdl.
7.36
0.00
42.42
0.88
bdl.
bdl.
31.63
bdl.
–
16.20

Chukanov et al.
(2016)

Zincoberaunite**(holotype)Tab. 2 Chemical analysis of zincoberaunite from Krásno (mean and 13 analytical points) compared with composition of the holotype samples of zincoberaunite, tvrdýite and Al-rich beraunite (wt. %)Zincoberaunite from Krásno near Horní Slavkov (Czech Republic)47

Jaromír Tvrdý, Jakub Plášil, Radek Škoda

Fe

zincoberaunite, Krásno
zincoberaunite, Hagendorf South (Chukanov et al. 2016)
Al-rich beraunite (Sejkora et al. 2016)tvrdýite (Sejkora et al. 2016)

AlZn

M2–M4 sites, the ratio of Al3+ to Me2+ in the M1 position
requires presence of divalent cations as follows:(Zn0.57Fe0.24Al0.19)Σ1.00(Fe3.85Al1.15)Σ5.00[(PO4)3.89(AsO4)0.10(SiO4)0.01]Σ4.00[(OH)4.59F0.24 O0.17]Σ5.00(OH2)4.00·2H2O. Notethat the empirical formula is a mean of 13 analyses.
With respect to the chemical heterogeneity of the sample,
zones with higher Zn content are expected to be closer tothe structural formula.
Figure 3 shows a close relation between the Zn–Alrich phases of the beraunite group from Krásno. As
evident from Tab. 2, the mean Zn content in the studied
sample of zincoberaunite is even lower than in the Al-richberaunite described by Sejkora et al. (2016). The difference most probably consists in the way how Zn is distributed over the four metal cation sites: while in tvrdýite
(and most likely also in associated Al-rich beraunite) Zn
enters the M1, M3 and M4 sites, in zincoberaunite it occupies predominantly the M1 site. On the other hand, theAl content in the holotype specimen of zincoberaunitefrom Hagendorf South is significantly lower.

Fig. 3 Comparison of zincoberaunitefrom Krásno with holotype zincoberaunite (from Hagendorf South) and related mineral phases from Krásno in the
Al– Fe–Zn ternary plot (apfu). Shaded
field refers to the detail shown in Fig. 5.

The EPMA results show a strong negative Al–Fe correlation as was also observed by Sejkora et al. (2016)
both in tvrdýite and in Al-rich beraunite from the same
locality (Fig. 4a). Contents of arsenic in the tetrahedral
sites are apparently lower (Fig. 4b) than those reported
by Sejkora et al. (2016) for Al-rich beraunite, but follow
the same negative correlation between P and As. The
positive correlation between Al and F is not evident; theF content in zincoberaunite is several times higher thanthat in Al-bearing beraunite (Fig. 4c). The biggest difference is in correlations of the pairs Zn–Fe and Zn–Al thathave been excluded in the Al-beraunite–tvrdýite series(Sejkora et al. 2016) but become very significant in thecase of individual zincoberaunite zones (Tab. 3). Individual zincoberaunite crystals exhibit chemical zonation
manifested by increasing Fe and decreasing Zn and Al
contents from cores to rims (Fig. 5).

4. X-ray crystallography and crystal
structure

Tab. 3 Values of Pearson correlation coefficient for 13 point analyses of zincoberaunite
Zn
Al
Fe
Si
As
P
F

48

Zn
1
0.70
–0.69
–0.17
–0.63
0.52
0.39

Al
–
1
–0.90
–0.17
–0.41
0.39
0.15

Fe
–
–
1
0.43
0.43
–0.59
–0.39

Si
–
–
–
1
0.06
–0.78
–0.03

As
–
–
–
–
1
–0.67
–0.36

P
–
–
–
–
–
1
0.25

F
–
–
–
–
–
–
1

A single crystal extracted fromthe studied specimen was used
for a single-crystal X-ray study
on a Rigaku SuperNova diffractometer with mirror-monochromatized MoK α radiation (λ =0.71073 Å) from a microfocus
X-ray source detected by anZincoberaunite from Krásno near Horní Slavkov (Czech Republic)

Fig. 4 Plots of Al vs. total Fe (a), As vs. P (b)and F vs. Al (c) for zincoberaunite in comparison with data published for tvrdýite and Al-richberaunite, all from the Huber open pit in Krásno.

3.0
2.8

(a)

zincoberaunite
Al-rich beraunite (Sejkora et al. 2016)2.6

tvrdýite (Sejkora et al. 2016)

apfu Al

2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

4.4

apfu Fe tot.

0.35

(b)

zincoberaunite

0.30

Al-rich beraunite (Sejkora et al. 2016)tvrdýite (Sejkora et al. 2016)

apfu As

0.25
0.20
0.15
0.10
0.05
0.00
3.70

3.75

3.80

3.85

3.90

3.95

4.00

apfu P
0.50
0.45

(c)

zincoberaunite
Al-rich beraunite (Sejkora et al. 2016)0.40

tvrdýite (Sejkora et al. 2016)0.35

apfu F

Atlas S2 CCD detector (Institute ofPhysics, Academy of Sciences of the
Czech Republic). Crystallographic
parameters and data collection details
are given in Tab. 4. Integration of thedata, including corrections for background, polarisation, Lorentz effects
as well as absorption were carriedout with the CrysAlis RED program(Rigaku 2018). The structure of zinco­
beraunite was solved independently
from the previous structure determination (Chukanov et al. 2016) using thecharge-flipping algorithm implemented
in the SHELXT program (Sheldrick2015) and subsequently refined by theleast-squares algorithm with Jana2006
software (Petříček et al. 2014) basedon F2. Nearly all atom sites were foundby the solution, missing positions of
the remaining O atoms, as well as
positions of the H atoms, were subsequently located from difference-Fourier maps. All atoms, except hydrogens,were refined using anisotropic atomic
displacement parameters (ADP). Isotropic atomic displacement parametersof the H atoms were set to be 1.2×Ueq(equivalent ADP) of the corresponding
donor O atoms. All cation sites wererefined as mixed (Zn + Al or Fe + Al)
sites based on the EPMA data andcrystal-chemical considerations. The
refinement converged to the final R(F)of 3.56 % for 1906 unique observedreflections. Atom coordinates anddisplacement parameters are given in
Tab. 5. The results of the bond-valence
analysis using bond-valence parameters from Gagné and Hawthorne(2015) are listed in Tab. 6.
The general structure architecture
is consistent with the previous structure determination by Chukanov etal. (2016) and in line with the general
structural features of beraunite-type
phosphate minerals (Moore and Kampf
1992). Nevertheless, the current study
provided a better resolution of thehydrogen-bonding network due to bet-

0.30
0.25
0.20
0.15
0.10
0.05
0.00
1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

apfu Al49

Jaromír Tvrdý, Jakub Plášil, Radek Škoda

Fe

25

in

6

ma
rg

7
3 5

30

70

10
12

re

4
11
9 13
2

co

35

65

1
8

Al

10

15

20

Zn

Tab. 4 Data collection and structure refinement details for zincoberaunite
Crystal data
Crystal system(Zn0.81Al0.19)(OH)2(Fe0.61Al0.39)(OH)2(H2[3]O)2(Fe1.52Al0.48)(H2[3]O)2(Fe1.72Al0.28)(OH)(PO4)3.83(AsO4)0.17(H2[4]O)2
monoclinic

Space group

C2/m

Unit-cell parameters: a, b, c [Å], β [°]20.3340(19), 5.1507(3), 19.1361(15), 93.568(8)Unit-cell volume [Å3]2001.3(3)Z

4Calculated density [g/cm3]

2.938

Crystal size [mm]0.072 × 0.016 × 0.009

F000

1754

Diffractometer

Rigaku SuperNova with Atlas S2 detector

Temperature [K]297

Radiation, wavelength [Å]MoKα, 0.71073 (50 kV, 30 mA)

Structure formula

Data collection

θ range for data collection [º]2.98−28.56

Limiting Miller indicesh = –27→26, k = –6→6, l = –25 → 4

Total reflections collected

13326

Unique reflections

2367

Unique observed reflections, criterion

1906, [I > 3σ(I)]Absorption coefficient [mm–1], type4.48; multi-scan

Tmin/Tmax

0.813/1

Structure refinement by Jana2006
Number of refined parameters, restraints,
constraints
R, wR (obs)Full-matrix least-squares on F2

R, wR (all)0.0576, 0.0491

Goodness of fit (obs, all)

1.60, 1.54

0.047

Rint

Weighting scheme, weights

0.0356, 0.0452

σ, w = 1/(σ2(I) + 0.0004I2)

Largest diffraction peak and hole [e /Å ]–50

202, 10, 57

31.18; 1.11

Fig. 5 Ternary plot of Al–Fe –Zn (apfu)
showing the zoning of zincoberaunite
crystals; the field extent is shown in
the plot in Fig. 3; numbers of points
correspond to Tab. 2.

ter quality of diffraction data.
The key feature of the zincoberaunite structure is a trimer offace-sharing octahedra centredby Fe4–M1–Fe4, forming thecore of the so-called h-clusterof Moore (1970). The trimers
are connected by corner-sharing
to the P1- and P2-centred tetrahedra and to pairs of cornershared Fe3-centred octahedra toform heteropolyhedral slabs coplanar with (100). These slabs
are interlinked via corner-sharing with (M2)O 2(OH) 2(H 2O) 2octahedra to form a 3D framework containing large ten-sided
channels along [010].
The water molecules represented by the O13 and O14 atoms are located in the channels
and are attached by the weak Hbonds to the framework (Fig. 6).
The structural formula obtained
from the refinement, based onrefined site occupancies andbond-valence considerations is(Zn 0.81Al 0.19)(OH) 2(Fe 0.61Al 0.39)( O H ) 2( H 2[3]O ) 2( F e 1.52A l 0.48)( H 2[3]O ) 2( F e 1.72A l 0.28) ( O H )( P O 4) 3.83( A s O 4) 0.17( H 2[4]O ) 2,

Atom
Zn1
Fe1
Fe2
Fe3
P1
P2
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
H1
H2
H3
O11H11aO11H11b
O13H13aO13H13b
O14H14aO14H14bx/a0.5
0.39153(2)0.54412(2)0.25
0.60569(4)0.40755(4)0.5
0.49287(11)0.47962(11)0.57393(10)0.30726(10)0.57694(11)0.37912(11)0.67872(10)0.59196(11)0.36989(11)0.25240(12)0.39944(11)0.61435(13)0.26923(14)0.5005(15)0.50.3014(15)0.2159(11)0.2564(17)0.6139(19)0.6147(18)0.3134(9)0.2496(18)y/b0.5
0.46294(9)0.22192(9)0.750.02461(13)−0.04401(14)0.3869(6)0.4557(4)−0.0482(4)0.2510(4)0.4814(4)−0.2375(4)−0.3137(4)0.0186(4)0.0605(4)0.1565(4)0.5897(4)0.0160(4)0.5156(4)0.8585(6)0.633(3)0.575(3)0.324(4)0.481(5)0.702(5)0.593(5)0.655(4)0.888(7)1.022(4)z/c
0.5
0.58521(3)0.67254(3)0.5
0.52510(4)0.68151(4)0.75
0.60582(12)0.66659(12)0.48003(11)0.53700(12)0.49810(12)0.66450(12)0.51567(12)0.60173(12)0.63573(12)0.40273(13)0.75929(12)0.68037(14)0.28461(17)0.6223(16)0.750.5108(15)0.3935(18)0.3642(12)0.7241(9)0.6484(11)0.275(2)0.275(2)Ueq
0.0123(2)0.00876(17)0.00812(17)0.0088(3)0.0071(2)0.0079(3)0.0192(11)0.0164(7)0.0168(7)0.0146(7)0.0171(7)0.0178(7)0.0171(8)0.0167(7)0.0222(8)0.0176(8)0.0225(9)0.0205(8)0.0297(9)0.0428(11)0.0196*0.023*
0.0205*0.027*
0.027*
0.0356*0.0356*
0.0513*0.0513*U110.0102(4)0.0089(3)0.0095(3)0.0079(5)0.0073(4)0.0093(5)0.025(2)0.0151(13)0.0127(12)0.0134(12)0.0147(13)0.0156(13)0.0180(13)0.0126(12)0.0215(14)0.0171(13)0.0226(15)0.0175(13)0.0332(16)0.0285(18)0.025(2)0.0151(13)0.0127(12)0.0134(12)0.0147(13)0.0156(13)0.0180(13)0.0126(12)0.0215(14)U220.0122(4)0.0069(3)0.0071(3)0.0067(4)0.0057(4)0.0065(5)0.0170(18)0.0167(12)0.0179(12)0.0122(11)0.0146(12)0.0143(12)0.0128(12)0.0148(12)0.0290(14)0.0133(12)0.0235(15)0.0265(14)0.0201(14)0.0469(19)0.0170(18)0.0167(12)0.0179(12)0.0122(11)0.0146(12)0.0143(12)0.0128(12)0.0148(12)0.0290(14)U330.0147(4)0.0106(3)0.0078(3)0.0118(5)0.0082(4)0.0078(5)0.0164(19)0.0171(13)0.0198(13)0.0182(13)0.0216(14)0.0239(14)0.0208(14)0.0228(14)0.0164(14)0.0223(14)0.0211(15)0.0173(13)0.0354(17)0.053(2)0.0164(19)0.0171(13)0.0198(13)0.0182(13)0.0216(14)0.0239(14)0.0208(14)0.0228(14)0.0164(14)U120.0022(3)0.0005(2)0.0001(2)−0.0002(3)0.0001(3)0.0002(3)00.0000(10)−0.0016(10)0.0013(10)0.0013(10)−0.0002(10)−0.0017(10)−0.0005(10)0.0041(11)−0.0022(10)−0.0036(11)−0.0017(11)−0.0030(12)−0.0006(15)00.0000(10)−0.0016(10)0.0013(10)0.0013(10)−0.0002(10)−0.0017(10)−0.0005(10)0.0041(11)U130.0032(3)0.0020(2)0.0007(2)−0.0003(3)0.0000(3)0.0000(3)0.0074(16)−0.0015(10)0.0016(10)0.0006(10)−0.0028(11)0.0036(11)0.0028(11)0.0029(11)0.0033(11)0.0004(11)0.0000(12)0.0002(11)−0.0008(14)0.0067(16)0.0074(16)−0.0015(10)0.0016(10)0.0006(10)−0.0028(11)0.0036(11)0.0028(11)0.0029(11)0.0033(11)U230.0006(3)0.0010(2)0.0004(2)0.0001(3)−0.0009(3)−0.0004(3)00.0031(11)−0.0042(10)0.0037(10)−0.0003(10)−0.0031(10)−0.0009(10)−0.0012(10)−0.0032(11)0.0045(10)−0.0008(11)−0.0053(11)−0.0044(12)0.0205(16)00.0031(11)−0.0042(10)0.0037(10)−0.0003(10)−0.0031(10)−0.0009(10)−0.0012(10)−0.0032(11)Z = 4. Although this formula is
not fully electroneutral (surplus
of 0.19 positive charges), we are
not able to elucidate the exact
charge-balancing mechanism,
which is most likely based onan OH↔O substitution. However, we are convinced that theformula can be considered asreliable. The site occupancies
should be viewed as the “bestproxies”, due to the similar scattering power of the substituting
elements Zn and Fe, and the factthat Al is most likely randomly
distributed over the all metalcation sites.
In the crystal structure ofzincoberaunite, there are three
distinct H2O molecules, in addition to five OH groups. TheseH2O groups play a different rolein the structure bonding. Oneof the classifications or typology of the molecular H2O in the
structures of inorganic solids
and minerals is based on theirrole in the structure bonding(Hawthorne 1994; Hawthorne
and Schindler 2008; Hawthorne2015). Particular types of H2O
can be distinguished based on
the coordination number of O
atoms in these H 2 O groups:
there are transformer, non-transformer, and inverse transformer
H2O groups with [3], [4], and[5]-fold coordinated O atoms,
respectively. In general, the roleof all types of molecular H 2O
in the structure is to transfer
the bond-valence from cations(corresponding to Lewis acids) to anions (corresponding toLewis bases). This action keeps
the structure, in particular of
hydrates of inorganic oxysalts,
together, as the strengths ofthese components are equal orsimilarly matching, thus following the valence-matching
principle of the bond-valencemodel (Brown 2009; Hawthorne
2012, 2015).

Tab. 5 Atom positions and displacement parameters (Å2) for zincoberaunite

Zincoberaunite from Krásno near Horní Slavkov (Czech Republic)51

Jaromír Tvrdý, Jakub Plášil, Radek Škoda

Tab. 6 Bond-valence analysis (valence units, vu) for zincoberaunite
Atom
Zn1
Fe1
Fe2
Fe3
T1
T2
H1
H2
H3
O11H11aO11H11b
O13H13aO13H13b
O14H14aO14H14b
∑

O1

O2
O3
O4
0.38×2→
0.40×2→
0.41
0.40
0.52
0.48
0.62

O5
0.67

O6
O7
0.36×2→
0.37
0.60

1.19

0.89

O9

O10

O11

0.58×2→
1.38

1.25

1.35
0.10
0.02

O13

0.50

0.39

1.34
1.29

1.26

0.10
0.09

0.96
0.94

0.14

0.05

0.98
0.94

0.04
0.11
1.41

2.15

2.09

1.99

2.16

O14

0.41×2→

1.28

0.91

O12

0.63
0.62

0.58×2→

0.88

O8

1.98

The three symmetrically distinct H2O molecules inthe structure of zincoberaunite actually represent two
distinct groups. While O11(Wa) and O13(Wa) are socalled transformer H 2O groups with [3]-coordinatedO atoms, O14(Wa), which is localised in the channels
running parallel to b, is a non-transformer group with a[4]-coordinated O atom (Fig. 7). In addition, three OH
groups help to propagate the bond-valence within theframework.

1.93

2.06

2.00

2.01

2.31

1.87

2.31

0.95
1.00
2.09

∑
2.28
3.08
3.13
3.14
5.16
5.18
0.98
0.91
1.01
1.05
1.08
1.04
0.98
1.06
1.00

5. Raman spectroscopy
Raman spectroscopy of zincoberaunite was undertaken on
the uncoated polished epoxy mount, by means of Horiba
LabRAM HR Evolution spectrometer (Masaryk UniversityBrno). This dispersive, edge-filter-based system, operatingin 180° backscattered geometry, was equipped with Olympus BX 41 optical microscope, a diffraction grating with
600 grooves per millimetre, and a Peltier-cooled, Si-based
charge-coupled device (CCD)
detector. The 633 nm He–Ne laser (3 mW at the sample surface)and 50× objective were selected
for spectra acquisition. Higher
laser powers caused damage ofthe analysed spot. Wavenumber
calibration was done using theRayleigh line and low-pressure
Ne-lamp discharge emissions.
The wavenumber accuracy was<0.5 cm–1, and the spectral resolution is ~2 cm–1 in the range
75–4000 cm–1. Band fitting wasdone after appropriate background correction, assuming
combined Lorentzian–Gaussianband shapes (Voight function)using PeakFit (Jandel Scientific
Software).
For holotype zincoberaunite,
only the infrared absorption
Fig. 6 The crystal structure of zincoberaunite from Krásno viewed down
the two-fold axis with displayed H-bonds; unit-cell edges are outlined in
red colour.

52

Zincoberaunite from Krásno near Horní Slavkov (Czech Republic)

Fig. 7 Hydrogen bonding in the structure of zincoberaunite. MX (X = 1–3) = octahedrally coordinated metal cations, Wa = H 2O molecule, OH =hydroxyl group; bond-strengths are given in valence units (vu).

spectrum was reported in the original description (Chukanov et al. 2016); Raman spectroscopy data have notbeen published so far. Comparison with Raman spectra of
related minerals of the beraunite group shows their mutual
similarity, but also distinct minor differences (Fig. 8).
Following interpretations are based on the vibrational
spectroscopic study of brownish beraunite performed by
Frost et al. (2014). In the high-energy region (Fig. 9),
the vibrational band at 3563 cm–1 can be assigned to thestretching vibration of the OH ions. Bands at 3418 and3261 cm–1 are attributed to stretching vibrations of symmetrically distinct hydrogen-bonded water molecules(Sejkora et al. 2016). The corresponding O–H···O hydrogen bond lengths calculated using the regression curveof Libowitzky (1999) are 2.81 and 2.73 Å; both values
are in good agreement with the hydrogen bond donor andacceptor distances in the Tab. 7.
In the range below 1300 cm–1 (Fig. 10), the strongest
bands at 999 and 1044 cm–1 are attributed to the ν1 symmetric stretching mode of PO43– and the bands at 1096,
1132 and 1156 cm–1 are assigned to the ν3 antisymmetricstretching vibrations of PO43– units (Frost et al. 2014; Sej­
kora et al. 2016). The weak bands at 935 and 873 cm–1 were
not reported in the beraunite pattern of Frost et al. (2014)

but they are present in the Raman spectrum of tvrdýite.
Sejkora et al. (2016) interpreted them as a manifestationof the δM–OH bending vibrations or H2O/OH libration
modes. A peak equivalent to the 935 cm–1 band occurs inthe spectrum of beraunite sample R060464 in the Rruff
Project website (Rruff Project 2019; pattern d in the Fig. 8);
in phosphosiderite (Scholz et al. 2013) this band is assigned
to a P–O stretching vibration of protonated phosphate units.
In the Raman spectrum of tvrdýite, unless there are otherinfluences, this could be due to the significant presence ofcomponents other than iron in the structure (Al, Zn, or AsO4
group). The series of Raman bands in the ranges of 681–569
cm–1 and 486–397 cm–1 are related to ν4 (δ) and ν2 (δ) bending
vibrations of PO4 groups, respectively. The bands at 364 and317 cm–1 are attributed to the M–O stretching vibrations.
The series of overlapping bands at 247, 208, 184, 136, 117
and 86 cm–1 are due to external or lattice vibrations (Frostet al. 2014; Sejkora et al. 2016).

6. Note on origin
According to Sejkora et al. (2006), the zone of occurrences of phosphate mineralizations in the Huber open
53

Jaromír Tvrdý, Jakub Plášil, Radek Škoda

dIntensity [a. u.]

c

b

a
1200

1000

800

600

400

Raman shi [cm-¹]
pit is exposed c. 20–40 m below the contact of the upper part of the greisenized stock with host gneisses, i.e.

200

Fig. 8 Comparison of the Raman spectra of zincoberaunite from Krásno andrelated minerals: a – zincoberaunite, Krásno, adjusted and smoothed;b – tvrdýite, Krásno (Sejkora et al.
2016), scale adjusted; c – beraunite,
Boca Rica, Minas Gerais, Brazil (Frostet al. 2014), scale adjusted; d – beraunite, York mine, Polk County, Arkansas,
USA (Beraunite R060464, Rruff Project2019), processed from the original
dataset; both c and d beraunite samples
have a brownish colour and their relation to eleonorite (later described member of the beraunite group) is not clear.

approximately 50–80 m below the original land surface
prior to mining.
At the late stages of hydrothermal activity, the primary
Tab. 7 Geometrical characteristics for hydrogen bonds (in Å and °) in the structure of zincoberaunite
phosphates (including fluorD–H···A
D–H (Å)H···A (Å)
D···A (Å)
D–H···A (°)
apatite and triplite) underwentii
O2–H1···O30.98(2)
1.91(2)2.828(3)
155(4)
metasomatic replacement (Sej­ii
O1–H2···O3
0.97(2)2.53(1)
3.332(3)
140(2)
kora et al. 2006). Subsequently,iii
O5–H3···O8
0.96(2)
1.89(2)2.787(3)
155(3)
corrosion cavities appeared reviii
O11–O11H11a···O10
0.93(2)
1.94(2)2.848(3)
164(2)
placing in-situ fluorapatite–
O11–O11H11b···O14
0.95(2)
1.76(2)2.690(4)
169(3)
triplite aggregates and a part ofO13–O13H13a···O7xv
0.93(2)2.18(2)
3.090(3)
167(2)
the dissolved elements released
O13–O13H13b···O9ii
0.95(2)2.31(2)3.204(3)
158(2)
from primary phosphates was
O14–O14H14a···O12xvi
0.94(2)
1.86(2)2.798(3)
174(3)
O14–O14H14b···O14xiii
0.94(3)2.10(3)
2.978(4)
155(3)
transferred to hydrothermal soSymmetry codes: (ii) x, y+1, z; (iii) –x+1, –y, –z+1; (viii) –x+1/2, –y+1/2, –z+1; (xiii) –x+1/2, y+1/2, lutions and later on precipitated–z+1/2; (xv) –x+1, y+1, –z+3/2; (xvi) x, –y+1, z–1/2. D – donor, A – acceptor
as secondary minerals in quartz
54

Zincoberaunite from Krásno near Horní Slavkov (Czech Republic)

Fig. 9 Raman spectrum of zincoberaunite from Krásno in the region 3800–3100 cm–1.

cavities. The typical assemblage of the corrosion cavities comprises phosphates such as kunatite (Mills et al.
2008), plimerite (Sejkora et al. 2011), iangreyite (Mills
et al. 2011) or krásnoite (Mills et al. 2012). According toobservations of the limited number of specimens available, it seems that beraunite-related minerals (tvrdýite,zincoberaunite) belong to remobilised secondary phasesthat typically occur in quartz cavities without any otherassociated minerals.
The high Al contents in the studied Al–Zn-richberaunite-related minerals from Krásno are in line with
abundant distribution of kaolinite-group minerals (mostof them unidentified; part of them are ascribed to dickite)in the gangue cavities (Sejkora et al. 2006). This suggests
a high activity of Al3+ in the parental aqueous solutions,in turn implying low pH conditions (caused by oxidationof the abundant arsenopyrite). These solutions underwent transport through the body of greisenized rocks
with abundant arsenopyrite, chalcopyrite and sphalerite;
therefore, they became enriched in As, Fe, Cu and Zn.
The solutions caused precipitation of various Fe–Zn–Cu
arsenates in quartz cavities (Vrtiška et al. 2018; Sejkora
et al. 2019a and references therein) or they interactedwith primary phosphates during transport; this enrichment in PO43– resulted in later crystallisation of secondary
phosphate minerals such as zincoberaunite. The observed
chemical zoning of the studied zincoberaunite (rimward

decrease in Al) indicates gradual evolution of the solutions towards more alkaline pH during zincoberaunite
crystallisation.

7. Conclusions
The phosphates of the beraunite group complete therich and rather variable association of late hydrothermal minerals in the Krásno–Horní Slavkov ore district.
The related Zn–Al-rich members of the beraunitegroup found in the now abandoned Huber open pit
show considerable compositional and crystalochemicalvariability, in particular in the occupancy of individual
structural positions. In this paper, attention is paid toaluminium-rich zincoberaunite, which is characterisedby selective zinc accumulation at the M1 site. Contrary
to expectations, however, trivalent aluminium also enters this position which is theoretically “reserved” fordivalent cations; the role of the di- and trivalent iron is
not entirely clear.
The studied zincoberaunite differs from the previously
described tvrdýite from the same locality. In the latter,zinc is contained in positions M1, M3 and M4 without
statistical predominance. Bulk Zn content in tvrdýite andassociated Al-rich beraunite approaches, or in some caseseven exceeds, that in zincoberaunite.
55

Jaromír Tvrdý, Jakub Plášil, Radek Škoda

Fig. 10 Raman spectrum of zincoberaunite from Krásno in the region 1300–75 cm –1.

Acknowledgements. The editor-in-chief Vojtěch Janoušek,
handling editor Jan Cempírek as well as both reviewers,
Uwe Kolitsch and Jiří Sejkora, are acknowledged forvaluable comments and suggestions that improved themanuscript. Special thanks go to Milan Gebouský, whokindly provided the sample. This work was financially
supported by the Grant Agency of Masaryk University,
Subprogramme Category A, Project MUNI/A/1387/2018,
and the Czech Science Foundation, Project GACR 1709161S.
Electronic supplementary material. Supplementary original crystallographic information file (cif) for the studied
zincoberaunite crystal is available online at the Journal
web site (http://dx.doi.org/10.3190/jgeosci.296).

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